Control valves whose housing is manufactured by a pressure die casting process have great friction hysteresis due to the mold inclines in the housing and the asymmetrical control edges arising in this way. As a consequence, an operating piston dips unilaterally into a bore hole in the housing owing to which a unilaterally transverse acting force arises during the action of pressure upon the operating piston. In this way, frictional force arises in the longitudinal direction that always works against an operating piston positioning force. This means that a differential pressure arises from the control valve when approaching a pressure point of a higher or lower pressure level. A difference in relation to the same specified value arises between rising and falling pressure. One thus speaks of a friction hysteresis. Owing to the mold inclines in the pressure die casting mold, great piston strokes additionally arise between the two positions control edge or ventilation edge that are completely open. With spring activated operating pistons, a great spring force difference arises due to the large operating piston stroke that leads to a rising or falling pressure course at different pressures.
The objective of representing a control valve that has a small friction hysteresis and, in this way, is especially suited for high standards of exactitude; and, moreover, at the same time offers an economical solution that is not susceptible to disturbance, forms the basis of the present invention.
The objective underlying the invention is accomplished by a representative control valve that also has the characterizing features of the main claim.